Hi @Yasmine DAIROU ,
Currently in Microsoft Q&A we only support English, could you please use English in the following description? Then we can help to solve your issues. And we are researching based on machine translation, I understand that you have a user who can send mail but not receive mail.
In this case, check if the Exchange Online Plan is enabled:
1.Sign in to the Microsoft 365 portal (https://portal.office.com) as an admin.
2.Click users, and then click active users.
Double-click the user. On the "Licenses and Apps" page, click to select the check boxes next to the items that you want to assign, make sure that exchange online plan is enabled.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.